Neuroepithelial bodies (NEB) and solitary endocrine cells in the hamster lung

Periodic acid-Schiff (PAS)-positive small-granule endocrine cells identified in serial plastic sections through 95% of the infracardiac lobe of a Syrian golden hamster lung were marked on a 70X cardboard reconstruction of the airways and recorded for computerized analysis as described in the preceding paper in this volume [1]. When airways were subdivided into thirds and the resulting small pieces of airway surface were analyzed statistically, endocrine cell loci appeared to be randomly distributed in the epithelial layer. Nevertheless, loci were absent from only 10 of 209 unit airways, far short of the 28 predicted from a random distribution. Solitary endocrine cells accounted for 37% of 980 loci but only 6% of all endocrine cells; 63% of loci consisted of endocrine cell clusters, broadly defined as "neuroepithelial bodies," of from 2 to 107 cells. Although small groups were preponderant, no significant discontinuity occurred in the size distribution between 1 and 56 cells per locus. Neuroepithelial bodies predominated everywhere, but especially in the lobar bronchus and at bronchioloalveolar portals, where cuboidal bronchiolar epithelium gives way to the attenuated epithelium of the respiratory zone; 45% were related to peribronchial smooth muscle and 18% to pulmonary capillaries. Only 3.3% of solitary cells were related to capillaries, 29% to airway muscle; 68% occurred in muscle-free regions of the airway, associated preferentially with ciliated epithelial cells. We conclude that endocrine cells are distributed in such a way that virtually all airways have at least one locus. This nonrandomness suggests that these cells are in fact important to normal lung function. Furthermore, because solitary endocrine cells and "neuroepithelial" cell clusters have different intrapulmonary distributions, they may well have distinct identities and functions.